This invention relates generally to heat pumps and refrigeration systems and more particularly, it relates to an apparatus and method for controlling continuously and discretely the speed of the compressor in response to load conditions while holding the speed of the indoor condenser fan motor at a constant full rated-speed when operating in the heating mode. The invention has particular applications in heat pumps for heating residential dwellings, small office buildings, mobile homes and the like.
It has been discovered that when a heat pump system is operated in the heating mode energy can best be conserved by varying the speed of the compressor in response to load conditions while maintaining the speed of the indoor condenser fan motor at its full rated-speed. If the heat pump cannot achieve the desired heating after the compressor speed has reached its full rated-speed, it has been found that the compressor can be designed to operate at speeds in excess of the rated-speed such as up to 150% of rated-speed or a 50% increase over rated-speed to supply additional heating prior to turning on of supplemental electric heaters. In this manner, considerable amounts of energy can be saved by maintaining the electric heaters in the off condition until it is necessary to turn them on to supply the desired heating.
After the compressor has been operated at such as 150% of rated-speed and the amount of heat is still insufficient, then a first stage of electric heat is turned on. If this first stage of heat is not adequate, second and third stages of electric heaters can be turned on additionally. The adding of the various stages of supplemental electric heaters is done progressively to achieve the desired amount of heating.